1. FIELD OF THE INVENTION
The present invention relates to an operating system for movable electrically powered bodies that run along a guide rail in a trolley system or a non-contact system. More particularly, this invention relates to a communication method in a movable body operating system, which is executed between movable bodies and a ground station.
2. DESCRIPTION OF THE RELATED ART
According to one conventionally proposed movable body operating system, one or a plurality of movable bodies run on a guide rail that is laid on a ceiling. Loads put on the movable bodies are conveyed together with the movable bodies, ensuring efficient distribution within a factory or a warehouse. A motor is generally used to move a movable body. A 3-phase AC supply voltage, which has a voltage of 200 volts (or 100 volts) and a frequency of 60 hertz or (50 hertz), is supplied to the motor via power supply lines (trolley lines) that are laid on the side of the guide rail.
There are two ways to supply electric power to each motor: the trolley system and the non-contact system. In the trolley system, a collector ring provided in each movable body contacts the power supply lines, and electric power is supplied to the movable body. Each movable body has a rectifier for rectifying the supplied AC supply voltage and an inverter for performing AC conversion of the rectified supply voltage and supplying the AC-converted supply voltage to the induction drive motor. The movable body further converts the AC supply voltage to a DC voltage in order to supply a drive voltage to the control unit for the induction motor.
In the non-contact system, a pickup coil is provided on each movable body at a position close to the power supply lines. As this pickup coil generates induced electromotive force, electric power is supplied to the movable body.
In the trolley system and the non-contact system, the driving of movable bodies is controlled based on an instruction signal from an operation control unit (so-called ground station). The ground station and each movable body are equipped with communication devices for effecting mutual communications necessary for operating the movable body. The trolley system employs a cable-based communication method, whereas the non-contact system may employ a cable-based communication method or a wireless communication method.
In the cable-based communication, a communication line (a trolley line for communications) is laid in parallel to the power supply lines along the guide rail. The communication line has one end connected to the ground station. The other end is contactable with the collector ring of each movable body. Accordingly, the movable bodies communicate with the ground station while running via the communication line.
When the guide rail is laid around a wide area, it takes considerable efforts and time in laying the communication line along the guide rail. Further, the collector ring and the communication line that contacts the collector ring will wear after a given time. This wear leads to improper contact between the communication line and the collector ring, which may cause communication failure. It is therefore necessary to regularly replace the communication line or each collector ring. Furthermore, laying the communication line along the guide rail inevitably enlarges the guide rail and complicates the shape of the guide rail.
In the wireless communication, when the guide rail is laid around a wide area, the ground station has a plurality of radio devices located at proper locations to reliably carry out wireless communication with the movable bodies. This requires a plurality of communication cables to electrically connect one ground station to the individual radio devices. The laying of the communication cables requires a great deal of labor and time. Further, it takes much time and effort to select the sites for the radio devices to ensure reliable communications with the movable bodies.